Outside of places like Detroit, Cleveland, or Pittsburgh there doesn't seems to be a big presence of major manufacturing or industrial output. It appears these places had there golden years decades ago, and the new manufacturing facilities you do see are spread out and are a lot smaller in size and operation when compared to those from 50 from 100 years ago.
What is the reason for this? Why don't they build massive factories like they use to? And why is there no high densiry of industrial buildings in a give area, anymore?